Abstract
Land plants evolved a long-distance transport system of water and nutrients composed of the xylem and phloem, both of which are generated from the procambium and cambium comprising vascular stem cells. However, little is known about the molecular mechanism of cell communication governing xylem-phloem patterning. Recently we identified a 12-amino acid peptide that suppresses tracheary element differentiation in a Zinnia xylogenic culture and designated TDIF (Tracheary element differentiation inhibitory factor). Here we show that TDIF is synthesized mainly in, and secreted from the phloem, and binds specifically to TDR (a leucine-rich repeat receptor-like kinase), whose expression is restricted to procambial cells. This signaling suppresses the differentiation of procambial cells into xylem cells, while promotes proliferation of procambial cells. Therefore this small peptide functions as a phloem-derived non-cell-autonomous signal that controls stem cell fate in the procambium.
